1. Field of the Invention
This invention relates to a navigation device for displaying current position information of a vehicle in map information to assist driving of the vehicle such as a car, and more particularly to a navigation device with means for storing route data of a traveled way through which the vehicle runs and passes, so as to display the route for driver's reference.
2. Description of the Prior Art
A vehicle navigation system using a navigation device which is mounted on a vehicle (hereinafter referred to as "navigation device") performs a navigation for a driver in a following manner. A current position of the vehicle is measured by a position-measuring means such as a GPS (Global Positioning System) or the like. Map information around the measured position and the current position of the vehicle which is momentarily shifting (changing) is displayed on the map in accordance with the measured current position of the vehicle. At the same time, a route data of a traveled route (way) through which the vehicle passed is stored in a memory so as to display the route extending to the current position together with the current position, as shown in FIG. 1.
In a case of driving a car, a driver travels to various destinations and frequently travels again to the destination to which he has once travelled. When a driver travels to a destination by a car, it is usual that the he does not completely remember the route to the destination even though he has previously travelled to the destination, and thus he has to travel to the destination for some times until he remembers the route and becomes able to travel to the destination without missing his way. Further, for a place to which he rarely travels, he forgets most of a route and is required to confirm the route to the destination by checking a map before or during his driving.
In view of the above problem, the inventors previously proposed an improved navigation device which is described in a Japanese Patent Application No. 3-218934. This navigation device stores the route through which a driver travels to a destination, and displays the stored route to the destination for driver's reference when he travels to the destination again.
FIG. 1 is a block diagram showing functions of the navigation device as described above. According to the navigation device, a current position measurement unit 102 measures the current position of a vehicle. Then, map information corresponding to the measured current position is outputted from a map data base 101 and the map information is displayed on a display unit 103 with the current position of the vehicle represented thereon. Simultaneously, a route management unit 104 stores the current position as a route data in a ring buffer, and displays a route to the current position as a normal route display (see arrow in display 3 of FIG. 1). In addition, the device stores route data between a collection start point and a collection termination point, each points is designated by an external command, in a reference route buffer together with information relating to the collection area. The route data stored in the reference route buffer is represented on the display 103 as a reference route data together with the map information when a driver instructs the display of the stored route data.
However, when a driver travels to a desired place along a way which he is not familiar to or he travels for the first time, he sometimes lose his way and takes the wrong way. In such a case, the above described navigation device stores and displays the route to the destination including the wrong way. This will be described with reference to FIG. 8A. In FIG. 8A, the point A represents a collection start point of route data and the point C represents a collection termination point of the route data. Now, it is assumed that a car runs from the point A to the point B, then returns to the point K, and then runs to the point B as indicated by arrows in FIG. 8A. In this case, even if the driver erroneously goes to the point B and returns to the point K, and then runs to the target point C, The above described navigation device stores the route data including the erroneous and unnecessary route data of going to the point B and returning back to the point K. If unnecessary route data such as the wrong way from the point K to the point B which is obtained by the erroneous running is directly displayed for driver's reference, he may drive the car along the erroneous way once again or be confused when he refers to the display. Therefore, such a route display has not been effectively used as a reference route display. Alternately, even if the running to the point B is not mistake, the route data of a half way from the point K to the point B is unnecessary.